Such contact members combined with printed resistances are used as sliding contacts and the like in electric/electronic circuits, so that particular mechanical properties such as springy characteristics, abrasion resistances and the like are required in order to keep electrical properties such as contact resistances and the like being stable when the sliding contacts are slid. For that purpose, it is desirable to employ noble metal members bearing less contact resistances and excellent abrasion resistances as such contact members. However, the noble metal members are usually welded only to contacts points on spring members used as base members in order to minimize costs of the contact members.
The contact points constituted in the above-mentioned way are formed into shapes being fitted to parts. Since it is essential that contact points are formed at the desired positions in order to ensure excellent contact performance and reliability between the contact points and the parts, it is required to weld noble metal wires precisely (within errors of ±0.2mm) on positions of the base members.
In presently widely used apparatuses equipped with seam welders, heat generated during welding steps cannot be properly controlled, so that defects such as deposits from works on electrodes, dust, burr, spatter, insufficient strength in welded portions, fluctuations of welded positions and the like are caused. Since appropriate measures against the generated heat are not taken, sufficiently precise welded semi-products required for succeeding steps such as slitting steps, stamping steps and the like cannot be obtained. In order to ensure the sufficiently precise welded semi-products, guiding holes are formed on the spring (base) materials, as a result a more complicated mechanism is required in a production apparatus. Consequently, a production rate, namely, a welding speed of merely ca. 3 m/H is obtained, so that high production costs are inevitable.
In order to produce highly reliable contact members at lower costs used as the electric/electronic parts such as sliding contacts and the like, noble metal wires and base metal hoops are welded at desired positions by a seam welding method. In this method, a spring member and a noble metal wire are welded as being held by upper/lower rotating electrodes. However, since energy supplied for welding flows to the electrodes, so that the electrodes are heated, which causes defects in welded portions.
In order to cool the heated lower rotating electrode, the electrode is partially immersed in cooling water, so that the upper electrode is indirectly cooled by welded materials cooled by the lower electrode (for example, see Ref. 1: Japanese laid open patent No. 9-106874).